1) FIELD OF THE INVENTION
The present invention relates to a composition for low hardness, fluorine-containing rubber, and more particularly to a composition for low hardness, fluorine-containing rubber comprising a solid fluorine-containing rubber and a liquid fluorine-containing rubber as main components and capable of producing a vulcanized product having a JIS A hardness, according to JIS K-6301, of not more than 50.
2) DESCRIPTION OF THE PRIOR ART
A vulcanized fluorine-containing rubber has good characteristics such as high heat resistance at an elevated temperature, high chemical resistance, high oil resistance, high weathering resistance, etc. and has a rapidly increasing demand in the fields of the automobile industry, the oil hydraulic industry, the general mechanical industry, the aircraft industry, etc. In addition to the above-mentioned characteristics of vulcanized fluorine-containing rubber, its low gas permeability and less generation of polluting substances have been recently recognized and its applications to gaskets, packings, etc. for electronic appliances have been now expected.
In the applications to packings for electronic appliances, a fluorine-containing rubber haying a low hardness, for example, a JIS (Japanese Industrial Standards) A hardness of not more than 50, is required. However, no vulcanized fluorine-containing rubber products having a JIS A hardness of not more than 50 and good rubber physical properties can be obtained only from an ordinary solid fluorine-containing rubber even without addition of carbon black or silica usually used as a reinforcing agent.
As to lowering the hardness of a fluorine-containing rubber, Japanese Patent Application Kokai (Laid-open) 62-277456 discloses a fluorine-containing rubber composition comprising a bromine or iodine-bonded, solid fluorine-containing rubber, which is cross-linkable by a peroxide or by radiation, and a liquid fluorine-containing rubber and further discloses that the composition is suitable for forming a low hardness, thin film.
Japanese Patent Application Kokai (Laid-open) 59-66442 discloses addition of a liquid fluorine-containing rubber to a fluorine-containing rubber composition containing carbon fibers, where an increased hardness encountered when the composition contains a large amount of an electroconductive filler is adjusted by a liquid fluorine-containing rubber.
However, as to the mold releasability in the injection molding where no external mold releasing agent is applicable and the adhesiveness of the resulting vulcanized product to a metal, the prior art is not on a satisfactory level yet.